A variety of devices for estimating the state of an engine have been proposed so far. For example, JP 2006-242146 A, hereinafter Patent Document 1, discloses a combustion pressure detector (inner-cylinder pressure detection means) is provided as an output measuring means. Provision of such a combustion pressure detector for each cylinder allows estimation of each cylinder's output based on a signal obtained from each combustion pressure detector.
However, providing the combustion pressure detector to each cylinder necessitates a cylinder block to be machined and such machining may cause structural fluctuations in the engine itself. Moreover, the combustion pressure detector is expensive and insufficient in strength. An object of the present invention is therefore to predict output (torque) characteristics of each cylinder with a simple arrangement.